New Mineral Named After GIA’s John Koivula
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 Post subject: Re: chrome tourmaline
PostPosted: Mon Mar 21, 2011 3:01 pm 
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Marco, at the very least it will improve your visual experience. It will be interesting to see how many filters you need to stack in front of your camera to completely eliminate reflection off the first surface of the stone.

Let us know how it turns out. A nice photo of the fluorescing tourmaline would be just the ticket to spice up this thread. :D


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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 8:12 am 
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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 8:19 am 
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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 8:20 am 
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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 8:26 am 
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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 8:27 am 
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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 8:29 am 
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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 8:42 am 
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Hi,

Thanks to Al Aoyama, I have somethings to show you of my effort with tourmaline and my spectrometer.
Unfortunately there is a color changer and a couple of other gems in the middle of this mixture of yellow green tourmaline that did not
make the cut, but I will try and post a copy of that later.

The "chrome" tourmaline that showed red under the filter is the shield cut and the curve below it is it's absorption
curve. The two rounds have their absorption curves below them and on is cuprian and the other is not. Care to hazard a guess
for now, based on the pictures? The beginning of the about 900nm curve on the far right of the graph indicates that the first round
is being colored by copper, while the second one is without copper as a chromophore.


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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 1:39 pm 
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Thanks, Bruce!
Very interesting and easy to see, with those pictures! 8)

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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 2:49 pm 
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hi Bruce

Now for comparison purposes, it is important to note that your absorption spectra are something like an upside-down version of my transmission spectra. That, and the the vertical scale of absorption is (I assume) plotted logarithmically with intensity vs. directly proportional to intensity in the transmission. Now, with that out of the way...

The shield cut's spectrum shows the absorption around 440 nm and 600 nm associated with the "green group" of chromium-bearing minerals. It does not show the classic narrow chromium absorption line one expects around 680 nm. But then I've sent a couple samples of Conny's chrome tourmaline to Barbra that also don't show that narrow absorption. Conny's samples do light up with the 400 nm laser, as Barbra can verify, so I would conclude that they are indeed colored by chromium. I am guessing this shield cut is the one that Bruce already had the chemical content analysed to show that chromium wasn't a factor. So it would be interesting to know if it does or does not light up bright red when you shine violet laser light upon it.

I think the violet laser light trick is about as close as we'll come for a simple, sure indicator of chromium. But for this to be so, it is critical to know how a deep green tourmaline that is known to not be colored by chromium reacts with the laser.

As for the copper, it is a brave man who knows that rise in absorption at 900 nm will also fall back down beyond that range. But if you've seen a lot of spectra, maybe it is ok not to worry about manganese or what-have-you. Does that green round seem to have that special glow people associate with copper?


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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 11:27 pm 
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Bruce sent me a pm that he meant to post publicly, so here it is...


bruce_tourm wrote:
Hi Brian,

Good questions. I think the software with the spectrometer can plot absorption with either a logrimaly or linearly y axis. I think the curves I posted are linear.

Yes the absorption curve is for the green shield cut tourmaline that does not indicate a significant amount of chrome in it's makeup. It did show a little over .1 wt percent V2O3. My question would be, even if the laser caused the stone to shine bright red would it prove that the chrome was the dominant chromophore.

Now for the brave part. The green round that has indications of copper does have a very bright look. The lack of a substancial 520 nm absorption peak indicates that the stone doen't have a significant amount of Mn+3. It is my understanding that only Mn+3 and not Mn+2 has some absorption around 900nm. I can post absorption curves for Rubellites that lack a significant absorption peak from iron at about 700nm and do indicate a very gentle increased absorption as the wavelength approaches 900nm. Considering my limitations I require that the point of inflection have a definite change in slope for the 900nm peak to indicate copper and that is of course that is only when there is the accompaning 700 absorption peak. Both need to be there to be copper. One final circumstantial point, the rough came out of Mozambique at the right time to have come from Mavuco.

I hope to have some more graphs soon.

Bruce


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 Post subject: Re: chrome tourmaline
PostPosted: Sun Apr 03, 2011 11:31 pm 
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And I replied...

Bruce, all that you wrote in the pm is good information...

With regards to the green shield tourmaline, from the numbers you posted, the amount of V2O3 is twenty times greater than the amount of Cr2O3. So I think that is a useful "null" test case. My guess is that the violet laser will not make it fluoresce red, or perhaps there'll be some weak fluorescence, but I don't know until the test is done.

I've seen the similar situation shining violet light on the green grossulars: those tsavorites colored by vanadium don't fluoresce at all, while those merelani mints colored by chromium do light up like crazy.

Also... really good description of how you evaluate the green round for copper. I recommend posting that information for everyone to see. I've read the article, but I had forgotten about looking for the peak on the low side of 700 nm. So your descriptions can help those who aren't familiar.

Looking forward to your other spectra. Always something interesting to see.


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 Post subject: Re: chrome tourmaline
PostPosted: Mon Apr 04, 2011 2:59 am 
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Great info!!

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 Post subject: Re: chrome tourmaline
PostPosted: Mon Apr 04, 2011 3:29 am 
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yeah, definitely! Thank you Bruce and Brian!!! =D> =D> =D>
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alberto

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 Post subject: Re: chrome tourmaline
PostPosted: Wed Apr 13, 2011 7:58 pm 
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More samples for investigation. I just sent Brian a box full of cut tourmaline and associated absorption curves. All of them show a 600 nm absorption peak according to my spectrometer. It will be very interesting to see if they glow under the violet laser so stay tuned. When the time comes I can supply pictures. You maybe surprised by what the tourmalines look like since I think that they are all the species Dravite, but I have no way of telling except for the oval "chrome" that has been tested and found to be Dravite.


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